"The governor has a lot of experience and grasp of trade issues, agriculture issues and the understanding of China," Jason Miller said during a routine conference call, adding that official announcement will come out later Wednesday.

"It's very clear that Governor Branstad is someone who'll represent our country well on the world stage," he said.

Branstad, an early supporter of Trump, met with the president-elect in New York Tuesday. He has accepted the offer, according to media reports.

"He's someone who has very much impressed President-elect Trump not just during the meetings but also on the campaign trail," Miller said, "We couldn't be prouder of the selection."

Branstad, 70, has long nurtured a close relationship with China, having visited China multiple times. He served as the governor of Iowa between 1983 to 1999, and again since 2011.

Iowa is now enjoying a tailwind from China's booming market. China is Iowa's fifth largest export market, and the state imported about 1.2 billion U.S. dollars in goods from China in 2011.